It is well known to utilize a mandrel positioned within a pipe to provide internal support to the pipe walls and thereby prevent buckling of the walls during bending of the pipe. Mandrels used for bending large diameter steel pipes of the type used for oil and gas pipelines (i.e., where the pipe diameter can exceed 48 inches and the pipe wall thickness can exceed one inch) are very large pieces of equipment which can weigh many tons. Such mandrels typically have powered wheels or treads which can be remotely controlled to facilitate the longitudinal movement of the mandrel within the pipe.
When bending large diameter pipe to create a curved section, it is common practice to perform a succession of small discrete bends at longitudinally spaced positions along the pipe. After each bend, the pipe is moved longitudinally through the bending apparatus until the location for the next desired bend is at the bending station. The mandrel must also be repositioned inside the pipe after each bend to provide support at the next bend position. During the course of such bending operations, the mandrel can be located fifty feet or more from the pipe end, and it is often out of sight of the person controlling it. Nevertheless, to achieve optimum results the mandrel must be accurately positioned with respect to the bending station, preferably within one inch of the desired location, when each bend is performed.
Typically, large mandrels are positioned within the pipe under the control of a dedicated mandrel operator who remains at the end of the pipe and sends movement commands to the mandrel by means of an electrical cable or similar direct control device. However, the mandrel operator typically has no way to directly determine the position of the mandrel with respect to the bending station. Instead, indirect measurements means must be used, such as determining the position of the pipe end relative to the bending station and then determining the position of the mandrel relative to the pipe end. The latter determination is often accomplished using a reach rod, i.e., a rigid pole of known length connected to the end of the mandrel and extending from the end of the pipe. After determining the estimated position of the mandrel with respect to the bending station, the operator sends movement commands to the mandrel until it has been moved into the desired position.
The use of a dedicated mandrel operator for positioning a mandrel within the pipe has numerous disadvantages. First, employing a dedicated mandrel operator represents a considerable expense to the pipeline contractor. Second, the positioning accuracy of the mandrel is dependent upon the skill and care of the mandrel operator and is subject to significant deviations caused by human error. Third, the speed of the bending operation is highly dependent on the skill and experience of the mandrel operator. For example, the weight of the mandrel results in considerable inertia which must be accounted for during movement, otherwise, the mandrel will "overshoot" the desired position. This can result in a time consuming series of back-and-forth movements each time the mandrel is repositioned. Finally, manual control systems require the human operator to stand along the line of motion of the heavy moving mandrel and pipe. A need therefore exists, for a system which can control the position of a mandrel within a pipeline without requiring a dedicated mandrel operator.
In view of the disadvantages inherent with manual control of the mandrel, systems for automatically positioning a mandrel within a pipe have been proposed. For example, U.S. Pat. No. 5,651,638 to Heggerud discloses an apparatus for controlling the position and operation of equipment within a pipeline. The Heggerud patent discloses and electromagnetic communication system including transmitting and receiving antenna external to the pipe for transmitting and receiving signals through the wall of the pipe to and from, respectively, receiving and transmitting antenna mounted on equipment within the pipe. The Heggerud patent discloses one approach to controlling the position of a mandrel within a pipeline, however, a need exists for alternative systems for automatically controlling the position of a mandrel within a pipeline.